Our purpose is to analyze how the primate brain develops, so as to provide a basis for understanding and treating the diseases of the nervous system that arise before birth. Work on the embryonic and fetal brain directly in primates is essential for this purpose because some structures are poorly developed or do not even exist in lower mammals. Our effort is concentrated on analysis of the development in man. The work on the human brain alone, however, provides only a basis for the posing of relevant questions, many of which can be answered only by application of experimental methods in monkeys. The fetal brains are processed by several specialized cytological methods, including autoradiography, Golgi staining, electron microscopy and histochemistry. Particular attention is given to the interactions of brain cells as they multiply and change positions relative to one another at early stages of development. These events appear to determine the fundamental patterns of cell interconnections, the "wiring" arrangements of the brain. The projects under study conern: 1) a neuron-glia relationship during cell migration; 2) the mode of cell migration to the superficial cortical layers; 3) the kinetics of proliferation and latency between final cell division and onset of differentiation; 4) the histogenesis of and synaptogenesis in occipital, frontal, and parietal cortices; 5) development of cortico-ponto-cerebellar system; 6) the histogenesis of the spinal cord; 7) computer-aided three-dimensional reconstruction and quantitative analysis of cellular volume and surface area from serial electronmicroscopic images; 8) factors influencing the shape of neurons and their assembly into circuits; 9) gliogenesis, and 10) the adaptation and development of new methods for ontogenetic analyses.